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Full text of "Solar energy system performance evaluation : Living systems, Davis, California"

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SOLAR/1046-79/14 




FEB 14 1980 




Solar Energy System 
Performance Evaluation 



LIVING SYSTEMS 
SINGLE-FAMILY RESIDENCE 

Davis, California 
October 1978 Through March 1979 



U.S. Department of Energy 

National Solar Heating and 
Cooling Demonstration Program 

National Solar Data Program 




NOTICE 

This report was prepared as an account of work sponsored by the United States 
Government. Neither the United States nor the United States Department of Energy, nor 
any of their employees, nor any of their contractors, subcontractors, or their employees, 
makes any warranty, express or implied, or assumes any legal liability or responsibility for 
the accuracy, completeness or usefulness of any information, apparatus, product or process 
disclosed, or represents that its use would not infringe privately owned rights. 



This report has been reproduced directly from the best available copy. 



Available from the National Technical Information Service, U. S. Department of 
Commerce, Springfield, Virginia 22161. 



Price: Paper Copy $5.25 
Microfiche S3.00 



SOLAR/1046-79/14 

Distribution Category UC-59 



SOLAR ENERGY SYSTEM PERFORMANCE EVALUATION 



LIVING SYSTEMS 
DAVIS, CALIFORNIA 



OCTOBER 1978 THROUGH MARCH 1979 



I. GRAY KINNIE, PRINCIPAL AUTHOR 

JERRY T. SMOK, MANAGER OF RESIDENTIAL SOLAR ANALYSIS 

LARRY J. MURPHY, IBM PROGRAM MANAGER 



IBM CORPORATION 
18100 FREDERICK PIKE 
GAITHERSBURG, MARYLAND 20760 



PREPARED FOR 

THE DEPARTMENT OF ENERGY 

OFFICE OF ASSISTANT SECRETARY FOR 

CONSERVATION AND SOLAR APPLICATION 

UNDER CONTRACT EG-77-C-01-4049 

H. JACKSON HALE, PROGRAM MANAGER 



TABLE OF CONTENTS 

Page 

1 . FOREWORD 1-1 

2. SUMMARY AND CONCLUSIONS 2-1 

2.1 Performance Summary 2-1 

2.2 Conclusions 2-1 

3. SYSTEM DESCRIPTION 3-1 

4. PERFORMANCE EVALUATION TECHNIQUES 4-1 

5. PERFORMANCE ASSESSMENT 5-1 

5.1 Weather Conditions 5-1 

5.2 System Thermal Performance 5-3 

5.3 Storage Performance 5-9 

5.4 Energy Savings 5-18 

6. REFERENCES 6-1 

APPENDIX A DEFINITIONS OF PERFORMANCE FACTORS AND SOLAR TERMS A-l 

APPENDIX B SOLAR ENERGY SYSTEM PERFORMANCE EQUATIONS B-l 

APPENDIX C LONG-TERM AVERAGE WEATHER CONDITIONS C-l 



n 



LIST OF ILLUSTRATIONS 



FIGURES 
3-1 

3-2 
5-1 
5-2 
5-3 
5-4 
5-5 

5-6 



TITLE 

Active Solar Domestic Hot Water System 
Schematic 

Passive Space Heating System 

Energy Flow 

Average Monthly Storage Temperatures 

Average Seasonal Comfort Levels 

Slab Storage Gradient vs. Insolation 

Slab Temperatures on a North - South Slice 
through House 

System Performance - January 29-30, 1979 



PAGE 
3-2 

3-3 

5-8 

5-11 

5-13 

5-14 

5-16 

5-17 



TABLES 
5-1 
5-2 
53 
5-4 
5-5 



LIST OF TABLES 

TITLE 
Weather Conditions 

Thermal Performance - Heating Season 
System Thermal Performance 
Storage Performance, Two Sample Days 
Energy Savings 



PAGE 

5-2 

5-4 

5-6 

5-10 

5-19 



in 



NATIONAL SOLAR DATA PROGRAM REPORTS 



Reports prepared for the National Solar Data Program are numbered under speci 
fie format. For example, this report for the Living Systems project site 
is designated as SOLAR/1046-79/14. The elements of this designation are 
explained in the following illustration. 



SOLAR/1046-79/14 



Prepared for the 

National Solar 

Data Program 



Demonstration Site 



Report Type 
Designation 



Year 



o Demonstration Site Number: 

Each project site has its own discrete number - 1000 through 1999 for 
residential sites and 2000 through 2999 for commercial sites. 






Report Type Designation: 

This number identifies the type of report, e.g., 

Monthly Performance Reports are designated by the numbers 01 (for 
January) through 12 (for December). 

Solar Energy System Performance Evaluations are designated by the 
number 14. 



IV 



Solar Project Descriptions are designated by the number 50. 

Solar Project Cost Reports are designated by the number 60. 

These reports are disseminated through the U. S. Department of Energy Technical 
Information Center, P. 0. Box 62, Oak Ridge, Tennessee 37830. 



Digitized by the Internet Archive 

in 2012 with funding from 

University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation 



http://archive.org/details/solarliving1979 



1 . FOREWORD 

The National Program for Solar Heating and Cooling is being conducted by the 
Department of Energy under the Solar Heating and Cooling Demonstration Act of 
1974. The overall goal of this activity is to accelerate the establishment 
of a viable solar energy industry and to stimulate its growth in order to 
achieve a substantial reduction in nonrenewable energy resource consumption 
through widespread applications of solar heating and cooling technology. 

Information gathered through the Demonstration Program is disseminated in a 
series of site-specific reports. These reports are issued as appropriate and 
may include such topics as: 

o Solar Project Description 

o Design/Construction Report 

o Project Costs 

o Maintenance and Reliability 

o Operational Experience 

o Monthly Performance 

o System Performance Evaluation 

The International Business Machines Corporation is contributing to the overall 
goal of the Demonstration Act by monitoring, analyzing, and reporting the 
thermal performance of solar energy systems through analysis of measurements 
obtained by the National Solar Data Program. 

The Solar Energy System Performance Evaluation Report is a product of the 
National Solar Data Program. Reports are issued periodically to document the 
results of analysis of specific solar energy system operational performance. 
This report includes system description, operational characteristics and 
capabilities, and an evaluation of actual versus expected performance. The 
Monthly Performance Report, which is the basis for the Solar Energy System 
Performance Evaluation Report, is published on a regular basis. Each parameter 
presented in these reports as characteristic of system performance represents 
over 8,000 discrete measurements obtained each month by the National Solar 



1-1 



Data Network (NSDN). Documents referenced in this report are listed in 
Section 6, "References." Numbers shown in brackets refer to reference numbers 
in Section 6. 

This Solar Energy System Performance Evaluation Report presents the results 
of a thermal performance analysis of the Living Systems solar energy system. 
The analysis covers operation of the system from October 1978 through 
March 1979. Living Systems solar energy system provides space heating, and 
domestic hot water to a single-family dwelling located in Davis, California. 
However, only the space heating subsystem will be discussed in this report. 
Section 2 presents a summary of the overall system results. A system descrip- 
tion is contained in Section 3. Analysis of the system thermal performance 
was accomplished using a system energy balance technique described in Section 
4. Section 5 presents a detailed assessment of the individual subsystems 
applicable to the site. 

The measurement data for the reporting period were collected by the NSDN [1]. 
System performance data are provided through the NSDN via an IBM-developed 
Central Data Processing System (CDPS) [2]. The CDPS supports the collection 
and analysis of solar data acquired from instrumented systems located through- 
out the country. These data are processed daily and summarized into monthly 
performance reports. These monthly reports form a common basis for system 
evaluation and are the source of the performance data used in this report. 

Acknowledgments are extended to those individuals involved in the operation 
of the Living Systems solar energy system: Johnathan Hammond, James Plumb, 
Brian and Catrina Tarkinson. Their insight and cooperation in the resolution 
of various on-site problems during the reporting period were invaluable. 



1-2 



2. SUMMARY AND CONCLUSIONS 

This section provides a summary of the performance of the solar energy system 
installed at Living Systems, located in Davis, California for the period 
October 1978 through March 1979. This solar energy system is designed to 
support the active preheating of domestic hot water and passive space heating 
loads; however, only passive space heating is covered in this report. A 
detailed description of the Living Systems solar energy system operation is 
presented in Section 3. 

2.1 Performance Summary 

The solar energy site was occupied 5 months of the season from November 1978 
through March 1979 and the solar energy system operated continuously during 
the entire reporting period. The total incident solar energy was 54.41 million 
Btu, of which 21.80 million Btu was collected by the solar energy system. 
Wood, another renewable resource, provided 4.65 million Btu toward the space 
heating load. Solar energy satisfied 79 percent of the space heating require- 
ments. The solar energy system provided fossil fuel savings of 37.18 million 
Btu. 

This performance level is reasonably close to the expected design performance; 
the differences in expected and actual performance can be accounted for by 
both the severe winter weather conditions encountered and by facets of owner 
interaction with the operation of the system. Some minor items are expected 
to be completed before next winter, after which the house should exceed its 
previous performance. 

Comfort levels in the major portions of the building were acceptable all 
season, but early morning chill was occasionally experienced in the bedrooms. 
The relative humidity was \/ery stable from day to day. 

2.2 Conclusions 

The Living Systems site has proven the concepts and received enthusiastic 
acceptance from the owners. The site was an early model. Subsequent systems 

2-1 



developed by the designers use passive hot water preheat systems, slab edge 
insulation and alternate methods for water tube anchoring. The primary 
backup heat system was a small, natural convection, natural gas heater; it 
was not used after February 18, 1979. For this reason, solar energy replaced 
79 percent of the heat that would have been required from natural gas, a 
nonrenewable resource. In addition, the owners bought two cords of wood for 
the wood stove, but used only one third of a cord. Weather-stripping the two 
rear doors and completing the anchoring of the insulating curtains should 
provide better performance next year. 



2-2 



3. SYSTEM DESCRIPTION 

The Living Systems site is a single-family residence in Davis, California. 
The home has approximately 1700 square feet of conditioned space. The solar 
energy system consists of two independently-controlled systems: an active 
system for preheating domestic-hot-water (DHW) and a passive system for space 
heating the home. 

The active solar DHW system has an array of flat-plate collectors with a 
gross area of 46 square feet. The array faces south at an angle of 45 
degrees to the horizontal. Potable city water is the transfer medium used 
throughout the system. In the event of freezing and no insolation, the con- 
troller drains the water from the collectors. When water in the collector is 
sufficiently warmer than the water in the preheat storage tank, the controller 
starts the circulation between the preheat tank and the collector. The preheat 
tank holds 82 gallons of water which is supplied, on demand, to a conventional 
20-gallon DHW tank. When the water preheated by solar energy is not hot 
enough to satisfy the hot water load, a natural gas burner in the DHW tank 
provides auxiliary energy for water heating. The system is shown schematically 
in Figure 3-1 . 

The passive solar space heating system is of the direct-gain type illus- 
trated schematically in Figure 3-2. Incident solar energy is admitted to the 
building through both the large south-facing vertical windows (approximately 
200 square feet) and the overhead skylight (approximately 80 square feet with 
a tilt of 60 degrees to the horizontal). Manually-operated insulating curtains 
provide insulation during the night and sunless days for the south-facing 
collector windows. Manually-operated insulating shutters also provide night 
insulation for the skylight glazing and are aluminum-coated to provide reflec- 
tion to the space below when open. Solar energy is stored in steel tubes 
that contain approximately 3600 gallons of water. The tubes are painted blue 
and placed near the south window wall and under the skylight. Additional 
storage is provided by the 6-inch-thick concrete slab floor of the building 
which is covered by brown ceramic tile. Collected solar energy is distributed 



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3-3 



by natural convection, by conduction through the slab floor, and by radiation. 
Floor covering is minimal: linoleum in the kitchen and eating area and white 
shag rugs in two bedrooms. The building envelope is well insulated in order 
to ensure energy conservation, with R-19 insulation in the walls and R-30 
insulation in the roof. The effective R-values of the windows are in the 
range of R-2 to R-10 (uncovered and covered with curtains and shutters). All 
glass surfaces are double-glazed with minimum window area in nonsouth-facing 
walls. Auxiliary space heating is provided by a gas-fired wall furnace which 
distributes the energy by natural convection. Additional auxiliary energy can 
be supplied from a wood-burning stove. 



3-4 



4. PERFORMANCE EVALUATION TECHNIQUES 

The performance of the Living Systems solar energy system is evaluated by 
calculating a set of primary performance factors which are based on those 
proposed in the intergovernmental agency report "Thermal Data Requirements 
and Performance Evaluation Procedures for the National Solar Heating and 
Cooling Demonstration Program" [3]. These performance factors quantify the 
thermal performance of the system by measuring the amount of energies that 
are being transferred between the components of the system. The performance 
of the system can then be evaluated based on the efficiency of the system in 
transferring these energies. A list of all performance factors and their 
definitions are listed in Appendix A. 

Data from monitoring instrumentation located at key points within the solar 
energy system are collected by the National Solar Data Network. This data is 
first formed into factors showing the hourly performance of each system com- 
ponent, either by summation or averaging techniques, as appropriate. The 
hourly factors then serve as a basis for the calculation of the daily and 
monthly performance of each component subsystem. The analysis technique used 
is outlined in the report, "Performance Evaluation Reporting for Passive 
Systems" [4]. The performance factor equations for this site are listed in 
Appendix B. 

Each month, as appropriate, a summary of overall performance of the Living 
Systems site and a detailed subsystem analysis is published. These monthly 
reports for the period covered by this Solar Energy System Performance Evalua- 
tion (October 1978 through March 1979) are available from the Technical 
Information Center, Oak Ridge, Tennessee 37830. 

In the tables and figures in this report, an asterisk indicates that the 
value is not available for that month; N.A. indicates that the value is not 
applicable for this site. 



4-1 



5. PERFORMANCE ASSESSMENT 

The performance of the Living Systems solar energy system has been evaluated 
for the October 1978 through March 1979 time period. Two perspectives were 
taken in this assessment: The first views the overall system in which the 
total solar energy collected, the system load, the measured values for solar 
energy used, and system solar fraction are presented. The second examines 
(in Section 5.4) the equivalent energy savings contributed by the solar 
energy system. 

The performance assessment of any solar energy system is highly dependent on 
the prevailing weather conditions at the site during the period of performance, 
The original design of the system is generally based on the long-term averages 
for available insolation and temperature. Deviations from these long-term 
averages can significantly affect the performance of the system. Therefore, 
before beginning the discussion of actual system performance, a presentation 
of the measured and long-term averages for critical weather parameters has 
been provided. 

5.1 Weather Conditions 

Monthly values of the total solar energy incident in the plane of the col- 
lector array and the average outdoor temperature measured at the Living 
Systems site during the reporting period are presented in Table 5-1. Also 
presented in Table 5-1 are the corresponding long-term average monthly values 
of the measured weather parameters. These data are taken from Reference 
Monthly Environmental Data for Systems in the National Solar Data Network [4]. 
A complete yearly listing of these values for the site is given in Appendix C. 

During October 1978 through March 1979, the average daily total incident solar 
energy on the collector window was 1095 Btu per square foot per day. This is 
below the estimated average daily solar radiation for this geographical area 
during the reporting period of 1176 Btu per square foot per day for a south- 
facing plane with a tilt of 60 degrees to the horizontal. The average ambient 



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temperature from October 1978 through March 1979 was 50°F as compared with 
the long-term average of 52°F from October through March. The number of 
heating degree-days for the same period (based on a 65°F reference) was 2978, 
as compared with the long-term average of 2471. 

Monthly values of heating degree-days are derived from daily values of ambient 
temperature and are useful indications of the system heating loads. Heating 
degree-days are computed as the difference between daily average temperature 
and 65°F. For example, if a day's average temperature was 60°F, then five 
heating degree-days are accumulated. The total number of heating degree-days 
is summed monthly. 

Daily analysis of wind speeds for the period shows that frequent peaks occurred 
which exceeded a 10 mph daily average with one peak at 18 and another at 
22 mph. Similar analysis of outdoor relative humidities indicated that 
"cold-dry" days are almost nonexistent in Davis, California. Only during the 
warmer days of October were there days with low humidity. 

Analysis of the weather conditions for the months November 1978 through 
March 1979 shows that winter was more severe than the long-term average: the 
incident solar energy was less, the temperature was lower and the resultant 
heating degree-days higher. 

5.2 System Thermal Performance 

The thermal performance of a solar energy system is a function of the total 
solar energy collected and applied to the system load. The total system load 
is the sum of the solar and auxiliary thermal energies delivered to the loads 
(excluding losses in the system). The portion of the total load supported by 
solar energy is defined as the solar fraction of the load. 

The thermal performance of the Living Systems solar energy system is presented 
in Table 5-2. This performance assessment is based on the 6-month period 
from October 1978 to March 1979. During the reporting period, a total of 



5-3 



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21.80 million Btu of solar energy was collected, a total of 22.33 million Btu 
of solar energy was used, and the total system load for space heating was 
28.30 million Btu. The discrepancy between solar energy used and solar 
energy collected is the excess heat available in storage at the beginning of 
November 1978. The measured system solar fraction was 79 percent as compared 
to an expected value of 88 percent for the winter season. 

In Table 5-1, note that the number of heating degree-days for November and 
December considerably exceeded the long-term average, but January had fewer 
heating degree-days than the long-term average. In Table 5-2, the heating 
load was highest in December rather than in January (as suggested by the long- 
term heating degree-day column in Table 5-1). The December weather was colder 
than January; the December insolation was also considerably lower than expected. 
Over the Christmas holidays, the relatively new wood stove overheated, causing 
the occupants to open windows and vent, and to operate the fan for several 
hours. Unfortunately, the vent remained open for several days, increasing the 
space heating load considerably. This emphasizes the cooperation required of 
the occupants of a passive home. By late January, the new owners (since 
November 1) were using minimum auxiliary, nonrenewable fossil fuel for heat. 
The last time fossil fuel was used was on February 18; the pilot light was 
turned off on March 4 to save energy. 

Table 5-3 contains additional information on thermal performance: The wood 
stove, using a renewable resource, reduced the apparent space heating load of 
the home. In October, the house was sometimes in the summer mode and sometimes 
heated by a part-time caretaker. In December, the wood stove was not used as 
often as in the other cold months and aggravated the severe weather load on 
the home. 

A total of 4.65 million Btu of auxiliary thermal energy was derived from use 
of the wood stove during the winter. According to the occupants, approximately 
one third of a cord of wood was used during the winter. Assuming a heat 
content of 30 million Btu per cord of wood, the wood stove provided energy at 
an average efficiency level of 47 percent. However, the sample size was too 
small to put much credence in this figure. The wood stove was used primarily 



5-5 



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to maintain a lower bound to the building temperature and interior comfort 
level. Therefore, the wood stove was used mostly at night and through the 
early morning and on cloudy days. 

In order to satisfy the building load, additional energy was derived from 
electric lights, appliances, etc. External lights for the yard, entryways, 
and garage did not contribute. 

For reporting purposes, the reported load is an equivalent equipment demand. 
As illustrated in Table 5-3, this space heating equipment demand is the 
difference between the building load and the wood energy gains. This demand 
is the amount of energy which would be required to maintain the measured 
building environmental conditions. Approximately 79 percent of this space 
heating subsystem demand was satisfied by collected solar energy. Only 5.97 
million Btu of auxiliary fossil fuel (natural gas) was used over the entire 
heating season. 

One more observation should be made from this table: While the external 
relative humidity was rather high, the internal relative humidity was stable 
near the bottom of the comfort zone. The occupants, however, have indicated 
complete comfort with this low relative humidity. 

The primary collection of incident solar energy at the Living Systems site 
occurs through the south-facing windows and skylight and goes directly to 
the water tube and concrete storage. Energy stored in the form of heated 
water or heated concrete is transferred to the air in the house by conduction 
and convection. This is shown graphically in Figure 5-1. The solar energy 
collection efficiency reaches a maximum near the coldest part of the year 
(mid-winter) and drops off rapidly in the fall and spring when there is 
relaxation of the rigid schedule of opening and closing insulating shutters 
and curtains, and when shading and venting to control overheating reduces 
the efficiency of energy collection. It is of particular interest to compare 
the conversion efficiencies of January, February, and March 1979: 70 percent, 
54 percent, and 40 percent, respectively. It should be noted that the value 



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of collection efficiency does not directly compare to the collection effi- 
ciencies presented for active solar energy systems, because the thermal 
losses that occur through the passive system glazing are a part of the 
building load instead of a part of the collection efficiency. 

5.3 Storage Performance 

Primary storage of collected solar energy at the Living Systems site is 
provided by the concrete slab floors of the building and the south and central 
water tubes. Evidence indicates that the gravel and earth below the slab 
provide additional storage (about twice the size of the slab). This storage 
would be even larger if the early version of the Living Systems homes had 
been constructed with slab-edge insulation as are the newer models. 

To compare the effectiveness of three storage areas, two contrasting days in 
January were selected: one with no insolation and one with very high insola- 
tion. In Table 5-4, on January 7, 1979, when the sun did not shine, the 
central and south water tubes experienced about the same temperature drop. 
However, the slab was the primary source of heating for the rear bedrooms. 
The conclusion is that the slab and sub-slab have large storage capacity and 
are more stable. On January 22, 1979, when the sun was at its hottest, the 
central water tubes had the largest temperature rise and the slab actually 
lost temperature. This loss reflects the continued drain from earlier days. 
The conclusion is that the water tubes are better collectors, while the slab 
is more involved in satisfying the space heating distribution. For this 
reason, as well as the problem with edge insulation, the average slab tempera- 
ture remains considerably below the water tube temperature. The seasonal 
view is shown in Figure 5-2. The water tube temperature is always several 
degrees above the slab temperature with the average temperature somewhere 
between them. In this plot, the three storage areas are averaged equally. 
Had weighted averaging based on the thermal capacity been used, the building 
storage temperature would be somewhat lower. 

Notice also that except in March when some very warm days were experienced, 
the average building temperature was always below the storage temperature. 



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5-11 



Fresh air enters this building primarily through infiltration. The cool 
outside air is heated by the energy stored in the water tubes and slab. 
Thus, the building temperature stays below the average storage temperature 
all winter. A clearer picture of this is apparent in Figure 5-3. Note that 
calculated comfort levels in zone 1, the front half of the building, and in 
zone 2, the bedrooms and master bath, are always higher than the building 
temperature. 

The comfort index used in this analysis is the operative temperature, which 
is defined as the average of the space dry bulb and mean radiant temperatures. 
For this analysis, the space mean radiant temperature is defined as the 
average surface temperature of all radiating surfaces bordering the space, 
except for the wood stove, since a surface temperature measurement of the 
wood stove was available for only a small portion of the season. The building 
is divided into two comfort zones: Zone 1 is the south part of the building, 
while zone 2 is the north part of the building. While relative humidity does 
play an important part in the perception of comfort, it is not presently 
included in the comfort index. Comfort levels in zone 2 were occasionally 
below those that would be acceptable for some individuals, but the owners are 
conservation conscious and accepted them. Comfort levels in zone 1 were 
normally acceptable. The occupants verified these observations. 

The earth around cellars can be used to keep them cool because the earth 
remains at 52 to 57°F year-round. However, when a warm surface such as a 
slab is placed on top of the earth, the thermal lag of the earth prevents 
rapid dissipation of the heat to the cooler subsurface. A volume of the 
earth under the slab acts as additional storage, moderating the heat of the 
house. In the Living Systems site, two sets of three sensors each were 
positioned to measure the temperature gradient across the slab storage: one 
sensor was placed one inch below the slab surface, one at six inches below 
the top of the slab and another at 11 inches below the top of the slab into 
the earth below the gravel. Figure 5-4 shows the plotted temperature values 
at these three locations together with a plot of the insolation values on a 
sunny January day. With sensors of this type, absolute values should not be 
considered; the shapes of the curves are of interest. As the sun came out, 



5-12 





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the slab surface started to heat almost immediately, the middle was delayed 
about two hours and the bottom was delayed about six hours. Although none of 
the areas of the slab were in the uncomfortable range at any time, the tem- 
perature swing on the top surface was about 5°F; whereas the temperature 
swing in the earth was only about 0.8°F. 

Taking another viewpoint, the Living Systems site is instrumented so that 
temperatures on a north-south slice through the house can be measured. 
Figure 5-5 shows temperatures one inch below the slab surface at 0800 (8 a.m.) 
and 1600 (4 p.m.) on the same day as the previous figure. The small water 
tanks moderate the edge temperature in the front, but also shade the front 
area of the slab. The large and small water tubes and front slab keep the 
largest part of the house warm. However, behind the partition, the tempera- 
ture drops rapidly toward the back wall. During this period, the rear center 
room shown on this chart was the coldest bedroom because of an open ceiling 
access. However, adjacent room slabs were almost only a few degrees warmer. 
As mentioned earlier, these homes now have edge insulation and this drop 
should be considerably less. 

With the aid of Figure 5-6, one can review typical operation of the Living 
Systems home over a two-day, January period; one day was sunny, the other 
mostly cloudy. In the early hours of January 29, 1979, the outside tempera- 
ture was below freezing and dropping. Storage and inside temperatures were 
also dropping with inside temperature somewhat chilly. Around 5 a.m. the gas 
heater came on and the building temperature started to rise. As the sun came 
up, the occupants opened the insulating shutters and curtains. The ceiling 
Casablanca fan was turned on for a little over an hour. During winter use, 
this fan distributes hot air which has risen, both naturally and from the 
heater; the fan also abstracts some heated air from the large water tubes. 
During the day, both storage and building temperatures rose. As the sun went 
down, the shutters and curtains were manually closed and the fan was turned 
on for almost an hour. The gas heater operated for short bursts through the 
evening and night and for two hours in the early morning. The shutters and 
curtains were opened during the short period when the sun was shining and 



5-15 




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Figure 5-6. SYSTEM PERFORMANCE - JANUARY 29-30, 1979 

LIVING SYSTEMS 
5-17 



some heat was gained. The wood stove was fired up from about noon until 5 p.m. 
and the fan was subsequently turned on. The storage and building temperatures 
were both higher at the end of the two-day period. Shutters, curtains, fan, 
wood stove and possibly the thermostat (not instrumented) were operated 
manually during the two-day period. 

5.4 Energy Savings 

Energy savings for the reporting period are presented in Table 5-5. The 
total savings were 37.18 million Btu, for a monthly average of 6.20 million 
Btu. 

Solar energy system savings are realized whenever energy provided by the 
solar energy system is used to meet system demands which would otherwise be 
met by auxiliary energy sources. 



5-18 



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5-19 



6. REFERENCES 

1. U.S. Department of Energy, National Solar Data Network , prepared 
under contract number EG-77-C-4049 by IBM Corporation, 
December 1977. 

2. J. T. Smok, V. S. Sohoni , J. M. Nash, "Processing of Instrumented 
Data for the National Solar Heating and Cooling Demonstration 
Program," Conference on Performance Monitoring Techniques for 
Evaluation of Solar Heating and Cooling Systems, Washington, D.C., 
April 1978. 

3. E. Streed, et. al . , Thermal Data Requirements and Performance 
Evaluation Procedures for the National Solar Heating and Cooling 
Demonstration Program , NBSIR-76-1137, National Bureau of Standards 
Washington, D.C. , 1976. 

4. "Performance Evaluation Reporting for Passive Systems", April 17, 
1979, SOLAR/0018-79/35. 

5. "A Thermal Performance Analysis Technique for Passive Solar Space 
Heating Systems" proceedings of the 3rd National Passive Solar 
Conference, January 11-13, 1979, San Jose, California. 

6. Mears, J. C. Reference Monthly Environmental Data for Systems in 
the National Solar Data Network . Department of Energy report 
SOLAR/0019-79/36. Washington, D.C, 1979. 

1 A Monthly Performance Report , Living Systems , SOLAR/1024-78/10, 
Washington, D.C, Department of Energy (October 1978). 

8.# Monthly Performance Report , Living Systems , SOLAR/1046-78/1 1 , 
Washington, D.C, Department of Energy (November 1978). 

9.# Monthly Performance Report , Living Systems , SOLAR/1046-78/12, 
Washington, D.C, Department of Energy (December 1978). 

10. # Monthly Performance Report , Living Systems , SOLAR/1046-79/01, 
Washington, D.C, Department of Energy (January 1979). 

ll.# Monthly Performance Report , Living Systems , SOLAR/1046-79/02, 
Washington, D.C, Department of Energy (February 1979). 

12. # Monthly Performance Report , Living Systems , SOLAR/1046-79/03, 
Washington, D.C, Department of Energy (March 1979). 

13.# "Users' Guide to the Monthly Performance Report of the National 
Solar Data Program," February 28, 1978, SOLAR/0004-78/18. 



#Copies of these reports may be obtained from Technical Information Center, 
P. 0. Box 62, Oak Ridge, Tennessee 37830. 

6-1 



APPENDIX A 
DEFINITIONS OF PERFORMANCE FACTORS AND SOLAR TERMS 



COLLECTOR ARRAY PERFORMANCE 

The collector array performance is characterized by the amount of solar 
energy collected with respect to the energy available to be collected. 

o INCIDENT SOLAR ENERGY (SEA) is the total insolation available 
on the gross collector array area. This is the area of the 
collector array energy-receiving aperture, including the 
framework which is an integral part of the collector structure. 

o OPERATIONAL INCIDENT ENERGY (SEOP) is the amount of solar energy 
incident on the collector array during the time that the col- 
lector loop is active (attempting to collect energy). 

o COLLECTED SOLAR ENERGY (SECA) is the thermal energy removed 
from the collector array by the energy transport medium. 

o COLLECTOR ARRAY EFFICIENCY (CAREF) is the ratio of the energy 
collected to the total solar energy incident on the collector 
array. It should be emphasized that this efficiency factor is 
for the collector array, and available energy includes the 
energy incident on the array when the collector loop is inac- 
tive. This efficiency must not be confused with the more 
common collector efficiency figures which are determined from 
instantaneous test data obtained during steady-state operation 
of a single collector unit. These efficiency figures are often 
provided by collector manufacturers or presented in technical 
journals to characterize the functional capability of a partic- 
ular collector design. In general, the collector panel maximum 
efficiency factor will be significantly higher than the col- 
lector array efficiency reported here. 

STORAGE PERFORMANCE 

The storage performance is characterized by the relationships among the 
energy delivered to storage, removed from storage, and the subsequent 
change in the amount of stored energy. 

o ENERGY TO STORAGE (STEI) is the amount of energy, both solar 
and auxiliary, delivered to the primary storage medium. 

o ENERGY FROM STORAGE (STEO) is the amount of energy extracted 
by the load subsystems from the primary storage medium. 



A-l 



o CHANGE IN STORED ENERGY (STECH) is the difference in the estimated 
stored energy during the specified reporting period, as indicated 
by the relative temperature of the storage medium (either posi- 
tive or negative value). 

o STORAGE AVERAGE TEMPERATURE (TST) is the mass-weighted average 
temperature of the primary storage medium. 

o STORAGE EFFICIENCY (STEFF) is the ratio of the sum of the energy 
removed from storage and the change in stored energy to the 
energy delivered to storage. 

ENERGY COLLECTION AND STORAGE SUBSYSTEM 

The Energy Collection and Storage Subsystem (ECSS) is composed of the 
collector array, the primary storage medium, the transport loops between 
these, and other components in the system design which are necessary to 
mechanize the collector and storage equipment. 

o INCIDENT SOLAR ENERGY (SEA) is the total insolation available 
on the gross collector array area. This is the area of the 
collector array energy-receiving aperture, including the frame- 
work which is an integral part of the collector structure. 

o AMBIENT TEMPERATURE (TA) is the average temperature of the out- 
door environment at the site. 

o ENERGY TO LOADS (SEL) is the total thermal energy transported 
from the ECSS to all load subsystems. 

o AUXILIARY THERMAL ENERGY TO ECSS (CSAUX) is the total auxiliary 
energy supplied to the ECSS, including auxiliary energy added to 
the storage tank, heating devices on the collectors for freeze- 
protection, etc. 

o ECSS OPERATING ENERGY (CSOPE) is the critical operating energy 
required to support the ECSS heat transfer loops. 

HOT WATER SUBSYSTEM 

The hot water subsystem is characterized by a complete accounting of the 
energy flow into and from the subsystem, as well as an accounting of 
internal energy. The energy into the subsystem is composed of auxiliary 
fossil fuel, and electrical auxiliary thermal energy, and the operating 
energy for the subsystem. 

o HOT WATER LOAD (HWL) is the amount of energy required to heat 
the amount of hot water demanded at the site from the incoming 
temperature to the desired outlet temperature. 



A-2 



o SOLAR FRACTION OF LOAD (HWSFR) is the percentage of the load 
demand which is supported by solar energy 

o SOLAR ENERGY USED (HWSE) is the amount of solar energy supplied 
to the hot water subsystem. 

o OPERATING ENERGY (HWOPE) is the amount of electrical energy 
required to support the subsystem, (e.g., fans, pumps, etc.) 
and which is not intended to directly affect the thermal state 
of the subsystem. 

o AUXILIARY THERMAL USED (HWAT) is the amount of energy supplied 
to the major components of the subsystem in the form of thermal 
energy in a heat transfer fluid, or its equivalent. This term 
also includes the converted electrical and fossil fuel energy 
supplied to the subsystem. 

o AUXILIARY FOSSIL FUEL (HWAF) is the amount of fossil fuel energy 
supplied directly to the subsystem. 

o ELECTRICAL ENERGY SAVINGS (HWSVE) is the estimated difference 
between the electrical energy requirements of an alternative 
conventional system (carrying the full load) and the actual 
electrical energy required by the subsystem. 

o FOSSIL FUEL SAVINGS (HWSVF) is the estimated difference between 
the fossil fuel energy requirements of the alternative conven- 
tional system (carrying the full load) and the actual fossil 
fuel energy requirements of the subsystem. 

SPACE HEATING SUBSYSTEM 

The space heating subsystem is characterized by performance factors account- 
ing for the complete energy flow into the subsystem. The average building 
temperature is tabulated to indicate the relative performance of the 
subsystem in satisfying the space heating load and in controlling the tem- 
perature of the conditioned space. 

o SPACE HEATING LOAD (HL) is the sensible energy added to the 
air in the building. 

o SOLAR FRACTION OF LOAD (HSFR) is the fraction of the sensible 
energy added to the air in the building derived from the solar 
energy system. 

o SOLAR ENERGY USED (HSE) is the amount of solar energy supplied 
to the space heating subsystem. 



A-3 



o OPERATING ENERGY (HOPE) is the amount of electrical energy 
required to support the subsystem, (e.g., fans, pumps, etc.) 
and which is not intended to directly affect the thermal 
state of the system. 

o AUXILIARY THER M AL US ED (HAT) is the amount of energy supplied 
to the major components of the subsystem in the form of thermal 
energy in a heat transfer fluid or its equivalent. This term 
also includes the converted electrical and fossil fuel energy 
supplied to the subsystem. 

o AUXILIARY ELECT RI CAL FUEL (HAE) is the amount of electrical 
energy supplied directly to the subsystem. 

o ELECTRICAL E NERGY SAVINGS {HSVE) is the estimated difference 
between the electrical energy requirements of an alternative 
conventional system (carrying the full load) and the actual 
electrical energy required by the subsystem. 

o BUILDING TEMPERATUR E (TB) is the average heated space dry bulb 
temperature. 

PASSIVE SYSTEM ENVIRONMENT 

In addition to the environmental summary performance factors presented 
earlier, additional performance factors describing the environment of a 
passive space heating system are presented. 

o BUILDING COMFORT ZONE 1 (C0M1 ) is an index relating to the com- 
fort conditions on the south side of the building. The index 
is formed as an average of the average dry bulb and mean radiant 
temperatures inside the sone. 

o BUILDING COMFORT Z ONE 2 (COM2) is an index relating to the 

comfort conditions on the north side of the building and is de- 
fined similarly to the other comfort index. 

o BUILDING TEMPERATURE MIDNIGHT (TMID) is the average building 
interior temperature at midnight local solar time. 

o BUILDING TEMPERATURE 6 A.M. (T6AM) is the average building 
interior temperature at 6 A.M. local solar time. 

o BUILDING TEMPERATURE NOON (TNOON) is the average building interior 
temperature at local solar noon. 

o BUILDING TEMPERATURE 6 P.M. (T6PM) is the average building 
interior temperature at 6 P.M. local solar time. 

o INTERIOR RELATIVE HUMIDITY (RELHIN) is the average relative 
humidity inside the building. 



A-4 



o AVERAGE STORAGE TEMPERATURE , (TST) is the mass weighted average 
temperature of all solar storage masses. 

o WIND DIRECTION (WDIR) is the average direction of the prevailing 
wind. 

o WIND SPEED (WIND) is the average wind speed measured at the site. 

o DAYTIME AMBIENT TEMPERATURE (TDA) is the temperature during the 
period from three hours before solar noon to three hours after 
solar noon. 

o RELATIVE HUMIDITY (RELH) is the average outside relative humidity. 



A-5 



APPENDIX B 
SOLAR ENERGY SYSTEM PERFORMANCE EQUATIONS 
LIVING SYSTEMS 



INTRODUCTION 

Solar energy system performance is evaluated by performing energy balance 
calculations on the system and its major subsystems. These calculations 
are based on physical measurement data taken from each sensor every 
320 seconds. This data is then mathematically combined to determine the 
hourly, daily, and monthly performance of the system. This appendix 
describes the general computational methods and the specific energy 
balance equations used for this site. 

Data samples from the system measurements are integrated to provide 
discrete approximations of the continuous functions which characterize 
the system's dynamic behavior. This integration is performed by summation 
of the product of the measured rate of the appropriate performance para- 
meters and the sampling interval over the total time period of interest. 

There are several general forms of integration equations which are 
applied to each site. These general forms are exemplified as follows: 
The total solar energy available to the collector Array is given by 

SOLAR ENERGY AVAILABLE = (1/60) l [1001 x AREA] x At 

where 1001 is the solar radiation measurement provided by the pyranometer 
in Btu per square foot per hour, AREA is the area of the collector array 
in square feet, Ax is the sampling interval in minutes, and the factor 
(1/60) is included to correct the solar radiation "rate" to the proper 
units of time. 

Similarly, the energy flow within a system is given typically by 

COLLECTED SOLAR ENERGY = E [Ml 00 x AH] x Ax 



where Ml 00 is the mass flow rate of the heat transfer fluid in lb /min and 
AH is the enthalpy change, in Btu/lb m , of the fluid as it passes through 
the heat exchanging component. 



m 



For a liquid system AH is generally given by 



AH = C AT 
P 



where C is the average specific heat, in Btu/(lb -°F), of the heat trans- 
fer fluid and AT, in °F, is the temperature differential across the heat 
exchanging component. 



B-l 



For an air system AH is generally given by 

AH = H (T .) - H (T. ) 

a v out a^ in' 

where H (T) is the enthalpy, in Btu/lb , of the transport air evaluated 
at the ^nlet and outlet temperatures or the heat exchanging component. 

H (T) can have various forms, depending on whether or not the humidity 
rcttio of the transport air remains constant as it passes through the heat 
exchanging component. 

For electrical power, a general example is 

ECSS OPERATING ENERGY = (3413/60) Z [EP100] x At 

where EP100 is the power required by electrical equipment in kilowatts 
and the two factors (1/60) and 3413 correct the data to Btu/min. 

These equations are comparable to those specified in "Thermal Data 
Requirements and Performance Evaluation Procedures for the National Solar 
Heating and Cooling Demonstration Program." This document was prepared 
by an interagency committee of the Government, and presents guidelines 
for thermal performance evaluation. 

Performance factors are computed for each hour of the day. Each integra- 
tion process, therfore, is performed over a period of one hour. Since 
long-term performance data is desired, it is necessary to build these 
hourly performance factors to daily values. This is accomplished, for 
energy parameters, by summing the 24 hourly values. For temperatures, 
the hourly values are averaged. Certain special factors, such as effi- 
ciencies, require appropriate handling to properly weight each hourly 
sample for the daily value computation. Similar procedures are required 
to convert daily values to monthly values. 



B-2 



EQUATIONS USED TO GENERATE MONTHLY PERFORMANCE VALUES 

NOTE: SENSOR IDENTIFICATION (MEASUREMENT) NUMBERS REFERENCE SYSTEM 
SCHEMATIC FIGURE 3-2 



AVERAGE AMBIENT TEMPERATURE (°F) 

TA = (1/60) x Z T001 x At 

AVERAGE BUILDING TEMPERATURE (°F) 

TB = (1/60) x l [(T600 + T601 + T602 + T603)/4] x At 

DAYTIME AVERAGE AMBIENT TEMPERATURE (°F) 

TDA = (1/360) x I T001 x At 

FOR + 3 HOURS FROM SOLAR NOON 

TIME OF DAY BUILDING TEMPERATURES (ONCE PER DAY) 

TMID = TB 

AT 12 HOURS FROM LOCAL SOLAR NOON 

T6AM = TB 

AT 6 HOURS BEFORE LOCAL SOLAR NOON 

TNOON = TB 

AT LOCAL SOLAR NOON 

T6PM = TB 

AT 6 HOURS PAST LOCAL SOLAR NOON 

INCIDENT SOLAR ENERGY PER SQUARE FOOT (BTU/FT 2 ) 

SE = (1/60) x I 1002 x At 

OPERATIONAL INCIDENT SOLAR ENERGY (BTU) 

SEOP = (1/60) x E [1002 x (192 * (D101 + D102 + D103) + 81 (D104 + D105 
+ D106))/3] x At 

HUMIDITY RATIO FUNCTION (BTU/lb -°F) 

HRF = 0.24 + 0.444 x HR 



B-3 



WHERE 0.24 IS THE SPECIFIC HEAT ANL HR IS THE HUMIDITY RATIO 
OF THE TRANSPORT AIR. THIS FUNCTION IS USED WHENEVER THE 
HUMIDITY RATIO WILL REMAIN TjNSTANT AS THE TRANSPORT AIR FLOWS 
THROUGH A HEAT EXCHANGING DEVICE OR AS IN INFILTRATION 
AVERAGE FLOOR STORAGE TEMPERATURE 

TSTSLAB = (1/1200) x E (T201 + T202 + T203 + T204 + T205 + 
T206 + T207 + T208 + T209 + T210 + T212 + T213 + 
T214 + T215 + T217 + T218 + T219 + T220 + T221 + 
T222) x At 
AVERAGE WATER STORAGE TEMPERATURE 

TSTST012 = (1/720) x E (T271 + T281 + T272 + T282 + T273 + 
T283 + T231 i 1241 + T232 + T242 + T233 + T243) 
SUM OF CONDUCTION LOSSES (U X A) 

LOSSES = HTN + HTS + HTW + HTE + HFL + HRF + EDGE LOSS + HSTECH 
ELECTRICAL HEAT INCIDENTLY APPLIED TO SPACE HEATING 

HAE = 56.8833 * (EP600 - OUTSIDE LIGHTS - EP100) 
SPACE HEATING SUBSYSTEM AUXILIARY NATURAL GAS FUEL ENERGY (BTU) 

HAF = 1000 * F400 
SPACE HEATING SUBSYSTEM AUXILIARY THERMAL ENERGY (BTU) 

HAT = 0.52 * HAF 
SPACE HEATING SUBSYSTEM LOAD (BTU) 

HL = LOSSES + HI - HAE - HFIRE 
INCIDENT SOLAR ENERGY ON COLLECTOR ARRAY (BTU) 

SEA = CLAREA x SE 

COLLECTED SOLAR ENERGY (BTU) 

SEC = SECA/CLAREA 



B-4 



COLLECTOR ARRAY EFFICIENCY 

CAREF = SECA/SEA 

CHANGE IN STORED ENERGY (BTU) 

STECH = WATERMASS * (TSTS012 - TSTST012 ) + 0.2 * SLABMASS * 

P 

(TSTSLAB - TSTSLAB ) 

WHERE THE SUBSCRIPT REFERS TO A PRIOR REFERENCE VALUE 

P 

SOLAR ENERGY TO LOAD SUBSYSTEMS (BTU) 

SEL = HSE 
SPACE HEATING SUBSYSTEM SOLAR FRACTION (PERCENT) 

HSFR = 100 x HSE/HL 
EXTERIOR RELATIVE HUMIDITY 

RELH = RH001/60 x Ax 
INTERIOR RELATIVE HUMIDITY 

RHIN = RH600/60 x Ax 
WIND NORTH - SOUTH COMPONENT 

WNS = V001 * COSD (D001)/60 x Ax 
WIND EAST - WEST COMPONENT 

WEW = V001 x SIND (D001 )/60 x Ax 
WIND VELOCITY 

WIND = V001/60 x Ax 
AVERAGE TEMPERATURE OF STORAGE (°F) 

TST = (1/60) x I (TSTSLAB + TSTST012)/2 x Ax 
SOLAR ENERGY TO SPACE HEATING SUBSYSTEM (BTU) 

HSE = HL - HAT 
HEAT OF INFILTRATION 

HI = VOLUME x 0.07216 x HRF x (TB - TA) * HINF 
WHERE HINF = AIR CHANGES PER HOUR 



B-5 



SPACE HEATING SUBSYSTEM FOSSIL ENERGY SAVINGS (BTU) 

HSVF = HSE/0.6 
SYSTEM LOAD (BTU) 

SYSL = HL 
SOLAR FRACTION OF SYSTEM LOAD (PERCENT) 

SFR = HSFR 
AUXILIARY THERMAL ENERGY TO LOADS (BTU) 

AXT = HAT 
AUXILIARY ELECTRICAL ENERGY TO LOADS (BTU) 

AXE = N.A. 
SYSTEM OPERATING ENERGY (BTU) 

SYSOPE = N.A. 
SYSTEM AUXILIARY FOSSIL ENERGY (BTU) 

AXF = HAF 
TOTAL FOSSIL ENERGY SAVINGS (BTU) 

TSVF = HSVF 
COMFORT INDEX ZONE 1 

COM1 = ((TSTSLAB + TSTSTOl )/2 + (T604 + T605 + T606)/3)/2 
COMFORT INDEX ZONE 2 

COM2 = (TSTST02 + (T601 + T602 + T603)/3)/2 
WIND DIRECTION 

WDR = ATAN (WEW, WNS) 

ADD OR SUBTRACT 360 TO GET BETWEEN AND 360° 



B-6 



APPENDIX C 
LONG-TERM AVERAGE WEATHER CONDITIONS 



This appendix contains a table which lists the long-term average weather 
conditions for each month of the year for this site. 



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